As conventional semiconductor memory, such as Flash memory and dynamic random access memory (DRAM), reach their scaling limits, research has focused on commercially viable low power, low operation voltage, high-speed, and high-density non-volatile memory devices. One example of such a non-volatile memory device is a variable resistance memory device including a programmable resistive memory material formed from a material exhibiting a very large negative magnetoresistance, often referred to as a so-called “colossal magnetoresistance” (CMR) material. The CMR material may be connected to a current controlling device, such as a diode, a field effect transistor (FET), or a bipolar junction transistor (BJT).
The resistance of the CMR material remains constant until a high electric field induces current flow through the CMR material, resulting in a change in the CMR resistance. During a programming process, the resistivity of the memory resistor at the high field region near the electrode changes first. Experimental data show that the resistivity of the material at the cathode is increased while that at the anode is decreased. During an erase process, the pulse polarity is reversed. That is, the designation of cathode and anode are reversed. Then, the resistivity of the material near the cathode is decreased, and the resistivity near the anode is increased.
One example of a CMR material is a manganese oxide of the general formula R1-xMxMnO3, wherein R is a rare earth element, M is a metal (e.g., calcium, strontium, or barium), and x is a number from about 0.05 to about 0.95. The CMR material is often referred to as “CMR manganites.” CMR manganites exhibit reversible resistive switching properties, which may be used for low power, low operation voltage, high-speed, and high-density memory applications.
PCMO is a CMR manganite that is currently being investigated for its potential use in variable resistance memory devices. Amorphous PCMO may be deposited using a variety of methods, such as physical vapor deposition (PVD), metal-organic chemical vapor deposition (MOCVD), spin-coating, and pulsed laser deposition. However, amorphous PCMO is not able to provide the requisite resistive switching for use in a variable resistance memory device. The resistive switching characteristics of PCMO have been shown to improve as the PCMO reaches a crystalline phase. In addition, amorphous PCMO is not well-suited for use in variable resistance memory devices because a poor yield is obtained. To convert amorphous PCMO to the crystalline phase, the amorphous PCMO may be exposed to temperatures of greater than about 400° C. For example, after depositing the amorphous PCMO using a conventional chemical vapor deposition (CVD) process, an annealing process is performed that converts the amorphous PCMO to crystalline PCMO, by exposing the amorphous PCMO to a temperature of about 525° C. Alternatively, an MOCVD process may be performed at increased temperatures (i.e., about 600° C.) to form the crystalline PCMO. However, PCMO materials formed at temperatures greater than 550° C. may exhibit decreased resistive switching characteristics. In addition, the high deposition temperature and high anneal temperature may damage other features of the variable resistance memory device, such as metal wiring and interconnects.
Variable resistance memory devices conventionally include a thin layer of crystalline PCMO, such as a crystalline PCMO layer having a thickness of less than about 50 nm. However, direct formation or growth of a PCMO layer that is both thin and crystalline is difficult to achieve because the crystallization utilizes a high temperature anneal, which may damage other components of the variable resistance memory device. The direct formation of the thin crystalline PCMO layer also affects its crystallization kinetics, which affects the properties of the resulting thin crystalline PCMO layer or avoids interfacial reactions with a bottom material of the variable resistance memory device. The resulting thin crystalline PCMO layer also causes significant stress in the variable resistance memory device.
It would be desirable to be able to produce PCMO materials that are both crystalline and thin (having a thickness of less than about 50 nm) for use in semiconductor memory devices.